Blood transfusion is the most common ICD-9-coded procedure performed in women during hospitalization in the United States. Transfusions are more frequent in women than men since the criteria for prescribing a transfusion often rests with threshold levels of hematocrit or hemoglobin which are normally lower in women. While transfusions have been considered life- saving in patients with significant blood loss, there is increasing evidence of immunomodulatory effects and thrombosis after transfusion. Unfortunately, there are no population-based reports on the characteristics of people who receive blood transfusions in the United States and little research regarding gender-specific outcomes during the post-transfusion period. A cohort study is proposed to examine the profiles of women and men who receive transfusions and gender- specific post-transfusion outcomes. Subjects will be a representative sample of Americans, ages 65 years and older, who were enrolled in fee-for-service Medicare programs. There are three specific aims: (1) to examine the variability in blood transfusion by subject characteristics, type of provider, and region in a representative sample of elderly Americans;(2) to assess the risk of infection after allogeneic blood transfusion in women and men;and (3) to assess the risk of thrombotic events after allogeneic blood transfusion in women and men. Linked files from the nationally-representative Health and Retirement Study (HRS) and the Medicare data will be used. This will include Center for Medicare and Medicaid Services (CMS) data for hospital stays, physician visits, home health services, skilled nursing facility stays, visits to outpatient clinics and ambulatory surgical centers, emergency department visits, hospice services, and clinical laboratory services from 1991 through 2007. Information regarding blood transfusion, infection, and thrombotic events (deep-vein thrombosis, pulmonary embolism, transient ischemic attack, stroke, and myocardial infarction) will be extracted from CMS files. Data regarding demographic information, lifestyle factors, disabilities, and medical history will be obtained from the HRS. Statistical analyses will involve weighting to account for the sampling design of the HRS and the results will be presented as national estimates of blood utilization for elderly women and men in the United States. Public Health Relevance: This study will provide the public, clinicians, and policy-makers with information regarding blood utilization, predictors of blood transfusion, and outcomes associated with blood transfusion in elderly women and men in the United States.